Metal carbonitride coatings

ABSTRACT

1. A PROCESS FOR COATING A SUBSTRATE WITH A SOLID SOLUTION CARBONITRIDE OF A METAL SELECTED FROM SILICONN, BORON, AND THE TRANSITION METALS IN GROUPS IVB, VB AND VIB OF THE PERIODIC TABLE COMPRISING: HEATING SAID SUBSTRATE TO A TEMPERATURE OF 400* TO 1200*C.; AND CONTACTING THE HEATED SUBSTRATE, IN THE ABSENCE OF HALOGEN, WITH A VAPOROUS ORGANIC COMPOUND HAVING THE GENERIC FORMULA ((R2)2N)NME WHEREIN ME IS ONE OF SAID METALS, N IS A VALENCE OF ME, AND R IS SELECTED FROM HYDROGEN AND HYDROCARBON RADICALS HAVING FROM 1 TO ABOUT 18 CARBON ATOMS, PROVIDED AT LEAST ONE R GROUP IS AT LEAST ONE OF SAID HYDROCARBON RADICALS.

United States Patent Q 3,846,162 METAL CARBONITRIDE COATINGS JohnAllison Bloom, Dallas, Tex., assignor to Texas Instruments Incorporated,Dallas, Tex. No Drawing. Filed Oct. 21, 1968, Ser. No. 769,385 Int. Cl.C23c 11/14, 13/00 US. Cl. 117-106 R 4 Claims ABSTRACT OF THE DISCLOSUREMetal carbonitride coatings, for example, titanium carbonitridecoatings, are applied to substrates by heating the substrates to theproper reaction temperature and thereafter contacting the substrateswith a vaporous stream containing a reactant compound which consistsessentially of carbon, nitrogen, hydrogen, and the metal, for example,tetrakis(dimethylamino)titanium.

This invention relates to coatings. In another aspect, this inventionrelates to vapor-deposited coatings of metal carbonitrides.

It has been found desirable to apply very hard, durable andoxidation-resistant coatings to the surfaces of various objects such asmissile nose cones, machine tools, turbine blades, and the like.

Thus, it is often desirable to utilize the basic properties of amaterial, but to protect the material from exposure to the environmentwithin which it must function. As mentioned in U.S. Pat. 2,972,556,carbon and graphite articles have exceptionally good thermal andelectrical properties. However, in some applications where the thermalcharacteristics of the material could be utilized, such as in a missilenose cone, the material oxidizes in the air under the high temperaturesto which it is subjected. The material must, for such application, becoated with a more oxygen-resistant material such as a metal carbide, ametal nitride, or both, as described in US. Pat. 2,972,556, mentionedabove.

Also, in the production of machine tools, for example, it is often moreeconomical to form a steel in the desired shape and coat with a hardermaterial such as tungsten carbide or titanium carbide. The diflicult andexpensive step of machining a dense, solid block of tungsten carbide ortitanium carbide into a desired shape is thus avoided.

It is known that coatings such as titanium carbide can be applied to asubstrate such as metal by exposing the surface of the metal to agaseous stream of titanium tetrachloride and methane. The metal isusually heated to a temperature between 900 C. and 1200 C. and uponcontacting the metal surface, the materials within the gaseous streamreact to form titanium carbide which will adhere to the surface of themetal. More specific details of this reaction may be found in US. Pat.2,962,388 and the description of equipment suitable for applying hard,dense coatings may be found in US. Pat. 2,884,894.

One of the problems encountered in coating metal with titanium carbideby the above-described process is the loss of temper in the metal.Generally, metals, and in particular steel, are first hardened byelevating the steel to about 1000 C. and then quickly quenched. Thesteel after quenching is tempered by elevating the temperature to about500 C. to 600 C. thus reducing its brittleness. If a hardened andtempered steel is then reheated to a temperature between 900 C. and 1200C. to permit the application of a coat of titanium carbide, the hardnessand temper of the steel is lost during the reheating process. If thesteel, after application of the coating, is quenched to again harden thesteel, the coating may be damaged as the steel will change in sizeduring the quenching process which can rupture the coating, create arough- 3,846,162 Patented Nov. 5, 1974 ness in the coating or cause itto eventually peel from the surface of the steel. Thus, not only is thecoating damaged, but the steel is also weakened and does not provide asstrong a support for the coating necessitating that the coating bethicker to withstand the forces to which it may be subjected.

Recently a process has been developed for coating substrates with asolid-solution carbonitride of a metal selected from silicon, boron, andtransition metals in groups IVB, VB and VIB of the Periodic Table, forexample, titanium carbonitride. This recently developed process isdescribed in co-pending patent application Ser. No. 694,390 filed Dec.29, 1967, now abandoned. This process can occur either at lowtemperatures, thus permitting the application of a hard coat to a metalwithout loss of hardness and temper which has been imparted to the metalby previous heating steps, or at higher temperatures for materialshaving compatible thermal behavior in any step required after thecoating operation. Not only can the metal carbonitride exhibit greaterhardness than materials such as titanium carbide or titanium nitride,but the deposition rate obtainable with the metal carbonitride is fromabout 2 to 10 times that of titanium carbide, for example. This processincludes the steps of heating the substrate to at least thedecomposition temperature of the reactants (generally from about 400 C.to about 1200 C.) and then passing a gaseous stream containing thereactants over the substrate to thereby yield the reactants at thetemperature of the body to permit the reaction of the metal, carbon andnitrogen, thereby forming a solid solution of the metal carbonitride onthe body. The reactants generally include a metal halide, e.g., titaniumtetrachloride, molecular nitrogen and/or an easily decomposablenitrogen-containing compound, an easily decomposable carbon-containingcompound (alternatively, an easily decomposable nitrogenandcarbon-containing compound can be used), and molecular hydrogen as areducing agent.

The metal carbonitride coating applied by this recently developed methodis a solid-solution material having the metal, carbon and nitrogenwithin a single phase crystal lattice. In addition to the great hardnessof the material, the strong bonding present gives a relatively largesurface energy to the material. This large surface energy is believed torender the material less likely to wet and adhere to the moltenmaterials such as glass, metals or alloys, after it is applied to asubstrate.

Even though this process for applying coatings of metallic carbonitridesyields improved products which are superior to the coatings heretoforeknown in the art, the process produces substantial amounts ofhalogencontaining contaminants such as solid halogen-containingcompounds which can deleteriously effect the coating. Additionally, acidby-products such as HCl are formed which can deleteriously effect thecoating and the substrate by destructive etching during deposition. Theflow of the reactants over the substrate must be controlled so that theby-products are removed as they are formed adjacent the substrate.However, it is generally very difficult to remove all of the acidby-product before destructive etching results during the deposition,particularly when the substrate being coated is a metal such as steel.

Therefore, one object of this invention is to provide an improvedprocess for coating a substrate with a metal carbonitride by vapor-phasedeposition in the absence of the conventional contaminatinghalogen-containing byproducts.

Another object of this invention is to provide an improved process forcoating a substrate with a metal carbonitride by vapor-phase depositionwherein the danger of destructive etching of the coating and/or thesubstrate by acid byproduct is eliminated.

According to this invention, a solid-solution carbonitride of a metalselected from boron, silicon, and the transition metals in groups IVB,VB and VIB of the Periodic Table is firmly coated on a substrate byvaporphase deposition with the use of a reactant compound consistingessentially of carbon, nitrogen, hydrogen, and the metal. The substrateis initially heated to a temperature at which the reactant compound willdecompose, and then the reactant is passed, in the vapor phase, over thesubstrate. The resulting decomposition of the compound on the substratewill yield carbon, nitrogen and metal atoms in the reactive state andpermit the reaction thereof to form the solid-solution layer of themetal carbonitride on the surface of the heated substrate.

The reactant compounds which can be used in the practice of thisinvention include organic compounds which consist essentially of carbon,nitrogen, hydrogen and the metal, and will decompose at the depositiontemperature, generally from the temperature within the range of from atleast about 400 C. to about 1200 C. or higher. A preferred group ofcompounds are represented by the formula [(R) N],,Me wherein Me isselected from silicon, boron, and the transition metals in groups IVB,VB and VIB of the Periodic Table as set forth on page B-2 of theHandbook of Chemistry and Physics, Chemical Rubber Company, 45th Edition(1964), n is a valence of Me, and R is selected from hydrogen andhydrocarbon radicals having from 1 to about 18 carbon atoms, forexample, alkyl, cycloalkyl, aryl, aralkyl, and provided that at leastone of the R groups is one of said hydrocarbon radicals.

An even more preferred group of reactants are the compounds of theabove-identified generic formula wherein Me is titanium, n is 4, and Ris selected from phenyl and alkyl groups having from 1 to about carbonatoms. Some specific examples of these preferred reactants includetetrakis(dimethylamino)titanium, tetrakis(diethylamino)titanium,tetrakis(dipentylamino)titanium, tetrakis (dioctylamino titanium,tetrakis (diphenylamino titanium, and the like.

The contact of the substrate with vaporous reactant can occur inconventional equipment. It is preferred that the substrate be suspendedin a reaction chamber and heated to a temperature at which the vaporousreactant compound will decompose when contacted therewith. Thus, thereaction temperature will vary depending upon the particular reactantcompound utilized but will generally fall within the range of about 400C. to about 1200 C. or higher. Next, a vaporous stream containing thereactant compound is passed over the heated substrate whereby thedeposition of the metal carbonitride on the substrate occurs. The rateof flow of the reactant compound over the substrate is generally notcritical and can be adjusted as desired in the particular coatingoperation. It is preferred that the vaporous reactant compound besuspended within a carrier gas which is nondeleterious to the reaction,such as, for example, nitrogen and/or hydrogen.

Various substrates can be coated by the process of this inventionincluding ferrous metals, titanium, ceramic materials, and refractorymaterials such as tungsten, molybdenum, niobium, and tantalum.

A better understanding of this invention can be obtained by referring tothe following illustrative example.

Example A graphite specimen substrate being approximately /2 inch byinch by 40 mils is supported on a graphite pedestal intermediate theends of the cylindrical steel reactor having a 6 inch I.D. An inletconduit having a 1 inch I.D. communicates through the top of the steelreactor and is positioned to discharge vaporous reactants at a pointabout 1 inch above the top of the substrate. The bottom of the reactoris fitted with an outlet conduit to permit exhaustion of gases admittedto and generated within the reactor in the coating process. Beneath thesubstrate is positioned a conventional resistance-heating device. Atemperature-sensing device is positioned directly above the substrate.The reaction chamber is evacuated and flushed with nitrogen, and thesubstrate is heated to about 1000 C. Next vaporous tetrakis(dimethylamino) titanium at a rate of 0.1 liters per minute and nitrogencarrier gas at a rate of 5 liters per minute are passed through theinlet conduit. The reactant stream is allowed to contact the substratefor about 15 minutes to about 2 hours. This contact will yield a hardcoating of titanium carbonitride on the substrate.

While specific terms have been used in describing some preferredembodiments of this invention, given for illustrative purposes only, andare not intended as limitations upon the invention.

What is claimed is:

1. A process for coating a substrate with a solid solution carbonitrideof a metal selected from silicon, boron, and the transition metals inGroups IVB, VB and VIB of the Periodic Table comprising:

heating said substrate to a temperature of 400 to 1200 C.; and

contacting the heated substrate, in the absence of halogen, with avaporous organic compound having the generic formula [(R) N],,Me whereinMe is one of said metals, n is a valence of Me, and R is selected fromhydrogen and hydrocarbon radicals having from 1 to about 18 carbonatoms, provided at least one R group is at least one of said hydrocarbonradicals.

2. The method of Claim 1 wherein said compound is tetrakis(dimethylamino) titanium.

3. The method of Claim 1 wherein said compound is tetrakis diethylamino)titanium.

4. The method of Claim 1 wherein said compound is tetrakis(diphenylamino titanium.

References Cited UNITED STATES PATENTS 3,356,618 12/1967 Rich et al.117-106 CX 3,382,113 5/1968 Ebert et al l17106X 3,386,866 6/1968 Ebertet al 117-106 X 3,432,330 3/1969 Diefendorf 1l746 OTHER REFERENCESDeitschrift Jtir anorganische und allgemeine Chemie, Vol. 198 (1931), p.260-261.

GEORGE F. LESMES, Primary Examiner W. E. BALL, Assistant Examiner US.Cl. X.R. 1l7106 C, 46 CG

1. A PROCESS FOR COATING A SUBSTRATE WITH A SOLID SOLUTION CARBONITRIDE OF A METAL SELECTED FROM SILICONN, BORON, AND THE TRANSITION METALS IN GROUPS IVB, VB AND VIB OF THE PERIODIC TABLE COMPRISING: HEATING SAID SUBSTRATE TO A TEMPERATURE OF 400* TO 1200*C.; AND CONTACTING THE HEATED SUBSTRATE, IN THE ABSENCE OF HALOGEN, WITH A VAPOROUS ORGANIC COMPOUND HAVING THE GENERIC FORMULA ((R2)2N)NME WHEREIN ME IS ONE OF SAID METALS, N IS A VALENCE OF ME, AND R IS SELECTED FROM HYDROGEN AND HYDROCARBON RADICALS HAVING FROM 1 TO ABOUT 18 CARBON ATOMS, PROVIDED AT LEAST ONE R GROUP IS AT LEAST ONE OF SAID HYDROCARBON RADICALS. 